Tread profile of a radial tire for motor vehicles

ABSTRACT

A radial pneumatic tire having a tread disposed on a carcass between its sidewalls and having an annular reinforcing member or breaker embedded between the tread and carcass is provided with a shoulder between the tread and each sidewall having a conical surface to facilitate steering a vehicle equipped with radial tires from one lane to a second lane which is on a level higher than the first one.

Maiocchi 1111 3,818,964 I 1451 June 25, E974 TREAD PROFILE OF A RADIALTIRE FOR 3,581,794 6/1971 Heuze 152/361 R MQTOR VEHICLES 3,667,5276/1972 Magistrimi and Maiocchi 152/361 R [75] Inventor: Luigi Maiocchi,Milan, Italy FOREIGN PATENTS APPLICATIONS Assigneez lndustrie Pirem IMilan Italy 1,414,773 12/1963 France 152/209 R [22] Filed: Nov. 9, 1972Primary Examiner-Robert J. Spar Assistant ExaminerKenneth Noland [21]Appl' 304%984 Attorney, Agent, or Firm- Stevens, Davis, Miller &

. Mosher 30] Foreign Application Priority Data Nov. 12, 1971 Italy31004/71 [57] ABSTRACT v A radial pneumatic tire having a tread disposedon a [52] US. Cl 152/209 R Y as w n its sidewalls and having an annular[51] int. Cl. ..'B60c 9/18 reinf r ing mem r or breaker embedded between[58] Field of Search 152/209 R, 361 th tr ad and ar ass is provided witha shoulder between the tread and each sidewall having a conical [56]References Cited surface to facilitate steering a vehicle equipped withUNITED'STATES PATENTS radial tires from one lane to a second lane whichis on 3,482,61 12/1969 French 152/209 R a level hgher than the 93,559,712 2/1971 Verdier 152/209 R 6 Claims, 10 Drawing Figures ti/////'0// 0C 1 ti III/1111 1 v 1 PAIENTED 5.818.964

sum 3 or s FlGb.

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I TREAD PROFILE OF A RADIAL TIRE FOR MOTOR VEHICLES This inventionrelates to a pneumatic tire for vehicles and more particularly to animproved radial tire.

The performance of radial tires on surfaces which vary abruptly inheight is not entirely satisfactory because of the tendency of suchtires to change their divehicle is substantially parallel to the edge ofthe elevated surface.

This disadvantage called ridge effect occurs both during movement of thevehicle between lanes of a highway which are at different levels, orwhen the vehicle must cross an elevated edge of the pavement as it movesfrom the highway shoulder to the paved surface.

This disadvantage is particularly apparent in radial tires because ofthe great difference in rigidity between the sidewalls or shoulders ofthe tire and the tire tread. In fact, while the tread portion of thetire is rather stiff, because it is supported by a breaker, thesidewalls are unsupported and are much more easily deformed. For thisreason the tire tends to follow alongside an elevated paved edge becausethe softer shoulder of the tire is depressed and the more rigid tiretread is not. High dynamic actions are exerted on the tire,-which isthence deflected from its steered course.

To eliminate this disadvantage, it has been proposed to providepneumatic tires with sidewalls having projections which cooperate withthe surfaces of steps or ridges in a roadway. However, such projectionshave not entirely solved the problem.

It is therefore an object of this invention to provide a radialpneumatic tire for vehicles such as motor vehicles which is devoid ofthe foregoing disadvantages. Another object of the invention is toprovide a radial tire adapted to move with less difficulty across theedge between two surfaces of different elevation. Another object is toimprove the performance of radial tires and particularly to provide aradial tire adapted to move over the edge between an unpaved surface orshoulder along a highway and a slightly elevated paved surface.

Other objects will become apparent from the following description withreference to the accompanying drawing wherein FIG. 1 is a diagrammatic,fragmentary perspective view of one embodiment of the invention;

FIG. 2 is a section taken along the line Il-II of FIG. 1.

FIG. 3 is a fragmentary section taken along the line III-III of FIG. 1;

FIG. 4 illustrates diagrammatically the profile of the external surfaceof a cross-section of an embodiment of the tire provided by theinvention;

FIG. 5 illustrates an enlarged portion of the shoulder of the tire ofFIG. 4;

FIG. 6 is a diagrammatic illustration of an embodiment of the inventionas it starts to cross the edge of the pavement from the shoulder of ahighway;

FIG. 7 is a fragmentary section of the tire shoulder taken along theline VlI-VII of FIG. 6; 1

FIG. 8 illustrates in a fragmentary section that portion of the tire ofFIG. 7 with the shoulder on the edge of the paved surface;

FIG. 9 is a diagrammatic illustration similar to FIG. 6 but after aportion of the tire is on the paved surface;

and

FIG. 10 is a perspective view of the lower part of an embodiment of theinvention as it moves up to the paved surface to the positionillustrated in FIG. 9.

The foregoing objects and others are accomplished in accordance withthis invention, generally speaking. by

' providing a radial tire which has a carcass with sidewalls, a treadextending laterally across the carcass between the sidewalls and anannular breaker embedded between the-tread and carcass with a conicalsurface which joins the tread and each sidewall and has an axis I whichis coincident with the axis of the tire.

Referring now to the drawing and particularly to FIGS. 1 and 2, theillustrated embodiment of a pneumatic tire has a carcass l of theradial'type in which the cords of the single plies lie in planes passingthrough the axis of rotation of the tire. A stiffening structure orbreaker 2 composed of one or more pair of plies or layers of cords isembedded between the curved wall of the carcass and a tread 3. Asuitable conventional rubber compound is applied over the externalsurface of the carcass 1 and breaker 2 to form tread 3 and sidewalls 4.

The external surface of tread 3 and of sidewalls 4, respectively 5 and6, are defined by the curved lines 5a and 6a on the plane of FIG. 2(which is a plane passing through the axis of the tire). Precisely, line5a is substantially concentric with the curvature of breaker 2 acrossits width. In this way, the thickness 11 of tread 3 over breaker 2 issubstantially uniform throughout the width of the breaker.

' In accordance with this invention, surface 5 of tread I 3 and eachsurface 6 of sidewalls 4 are joined by means of a substantially conicalsurface 7 (FIGS. 1 and 2) which has an axis which coincides with theaxis of the tire. The intersection of each surface 7 with a planepassing through the axis of the tire (plane of FIG. 2) originatessegments 7a (FIG. 4). Segments 7a intersect thecurved lines 5a and 6a asdefined above at points P and P respectively, as shown in FIG. 4. Onlythe profile 5a of the external surface 5 of tread 3 is illustrated inFIG. 4 for the purpose of clarity.

Each conical surface 7 (FIG. 2) is selected in such a way that the anglea (FIG. 4) formed between tangent t to curve 5a at point P and thecorresponding segment 7a (coincident with a generatrix of said conicalsurface) is between 15 and 50.

The reasons which have led to this selection of the value of angle a inthe above range will be more clearly apparent from the followingdiscussion.

The tread 3 (FIG. 2) is provided with annular grooves 9 and spacedprojections 8. Grooves 9 are of substantially the same depth and a line9a drawn through the base of grooves 9 is concentric with the profile oftread 3 as represented by the dotted line 9a in FIGS. 2 and 4.

Each conical surface 7 (FIG. 2) intersects sidewall 4 at the point wheregroove 9 crosses the external surface 6 of sidewalls 4. In other words,curve 9a (FIG. 4) passes through points P Each surface 7 is providedwith an annular groove 11 (FIGS. 1, 2 and 3), arranged substantially inthe central part of the surface itself. The revolution surface whichdefines saidgroove, crossing a plane passing through the axis of thetire (plane of FIGS. 2 and 4), generates a curved line 11a (FIGS. 4 and5), shaped for instance as an arc of circumference.

The dimensions of annular groove 11 are such that the ratio between itsdepth a (FIG. 5), measured in a direction perpendicular to segment 7a,and its width b, measured in a direction parallel to said segment, fallswithin a pre-established range. The value of the ratio a/b is between0.2 and 0.5. Also the ratio between width b of the annular groove andlength c of the segment 7a (FIG. 5) falls within a pre-establishedrange. The value of said ratio b/c is between 0.3 and 0.6.

Each conical surface 7 is provided with a plurality of radial grooves 12(FIGS. 1 and 3), each of which has a concave surface 13. Said grooves 12are uniformly spaced circumferentially on each surface 7 and the axis ofeach of them is substantially contained in a plane passing through theaxis of the tire.

The width of the breaker 2, indicated as L in the diagrammaticalrepresentation of FIG. 4, is greater than the distance L between thepair of parallels which define externally the upper surface (FIG. 2) oftread 3 and whose path has been indicated with dotted line '1, in FIG.4.

Moreover, width L is smaller than distance L between the pair ofparallels which define axially externally the annular grooves 11, andwhose path has been indicated with 1 in FIG. 4.

According to a preferred constructional arrangement, width L of breaker2 is greater than distance L as defined above and smaller than distanceL between the pair of parallels which define axially internally saidannular grooves, and whose path is indicated with 1 in FIG. 4.

The tire provided by this invention behaves as follows when installed ona motor vehicle.

Let us'assume that the vehicle equipped with the tires according to theinvention is to move from one running lane of a highway to another oneand that the level of .the two is different so they are separated fromeach other by a step or elevated edge 14 (FIGS.'6, 7 and 8).

Moreover, let us assume that during this movement, the angle [3 (FIG. 6)formed in the running direction of the tire 15 towards the edge 16 ofstep 14 is very small, for instance 5. At the beginning of contactbetween tire 1 5 and edge 16, (FIG. 7), the latter takes place at onegeneratrix of the conical surface 7, which, at the time in which saidcontact takes place, forms with respect to the vertical face 17 of step14 an angle If 8 is the value of the angle formed by tangents t, (FIG.4)

at point-P with the axis of the tire, the value of angle 7 is equal to:

Consequently, angle y depends on a and its value, with 8 constant(namely at a curvature equal to that of the curved line 5a (FIG. 4)) isthe higher the smaller the value of a. From FIG. 7 it is evident that itis in- .creasingly easier for tire 15 to move to step 14 as the value of7 increases. It has been ascertained that, with difference valuesbetween the maximum width of the tire section and the useful width ofthe tread which are comprised in the range normally adopted inconventional tires and with commonly adopted 8 values, if the value ofangle a is comprised in the above indicated range, the conical surfaces7 are able to allow an easy stepping up of the tire 15 on the step 14.

In the conventional tires heretofore known, in which theconical surfaces7 are not provided,the contact between the step and the tire takes placebetween surface 17 (FIG. 7) of the step itself and the surface of thetire sidewall, which form very reduced angles between them. In theseconditions it is difficult for the tire to step up to step l4 because ofthe high pressures which the surface of the step applies to the tiresidewall, and which tend to detach the latter from the former.

Also the annular grooves 11 (FIGS. 1, 2 and 3) facilitate in aremarkable way the stepping up of the tire on the step.

In fact, during said phase, the groove 11 (FIG. 8) even if it isdeformed as shown in FIG. 8, constitutes a cavity into which edge 16 ofthe step is received. Between the deformed surface of the groove and theupper face of step 14 pressures substantially normal to said face(indicated with the vectors of FIG. 8) are transmitted, which obviouslycooperate in supporting the tire during the stepping up phase.

This action, carried out by the annular grooves 11, is

particularly relevant when the crossing of the step is effected at asmall angle B (FIG. 6), namely when the angle formed between the edge 16of the step and the running direction of the vehicle is small.

An action analogous to that described above is exerted by the grooves 12(FIGS. 1 and 3), which are also able to facilitate the stepping up ofthe tire on a step, in particular when the .crossing of the step iseffected at rather high '3 angles, for instance angles greater than 5,as it is diagrammatically represented in FIG. 9. In this case, becauseof the deformation of the surfaces 13 (FIG. 10) of grooves 12, thegrooves 12 cooperate with the upper face 18 of the step and pressuressubstantially normal to the face are transmitted between the latter andthe surfaces, which pressures are able to contribute to the support ofthe tire during its stepping up on the step.

The above described actions carried out by the conical surfaces 7, theannular grooves 11 and the grooves 12, are most pronounced if the widthof the breaker 2 is within the range indicated hereinbefore.

If the width of breaker 2 is such that its ends are radially below asubstantial portion of the conical surface 7, the deformability of thelateral parts of tread 3 (FIGS. 2 and 3) and of the parts of sidewallsexternal surfaces 6 adjacent to surfaces 7 is considerably reduced,andis substantially of the same order of magnitude as that existing atthe central part of the tread. It follows that, during the stepping upof the tire on the step, in the zone of contact of the tire with thestep, local deformation is not very high so that a correct contactbetween the conical surfaces 7 and the step is insured, and above allthere are not sudden variations of rigidity when the contact between thetire and the step passes from a conical surface 7 to the surface 5 oftread 3.

As it is known, sudden variations of rigidity cause dynamic actions onthe tire, which can cause unexpected deviation of the vehicle from itspath.

Another favorable action exerted by the breaker 2, when its width L iswithin the above indicated range of values, is that heating of the zonesadjacent to the conical surfaces 7 during the normal running of thevehicle is reduced. In fact, if width L of the breaker is rather high,the lateral parts of the breaker prevents an excessive deformation ofthe material forming the lateral parts of the tread 3 and of those partsof sidewalls 4 which are between the breaker itself and the conicalsurfaces 7.

To realize that the action carried out by breaker 2 is obtained only ifits width L is within the range of values indicated above, it isnecessary to take into account that, if the value of L is too low(smaller than the indicated one), the lateral parts of tread 3 are notsufficiently stiffened and, during the working of the tire, cantherefore deform excessively, giving rise to'a premature wear, while, ifthe value of L is too high (greater than the indicated one), the treadcan detach from the breaker because of the fatigue stresses to which thetire is subjected in use. In fact, for values of L higher than thoseindicated, the resistance of the material which is between the edges ofbreaker 2 (FIGS. 2 and 3) and the surfaces 6 of the sidewalls is reducedconsiderably because of the small thickness of the material itself.

It is pointed out that both the annular grooves l l and the grooves 12cooperate in limiting the heating of the lateral parts of tread 3between the conical surfaces 7 and breaker 2, since those groovesrepresent a wide surface through which a thermal exchange may take placebetween the material constituting said parts and its environment.

lt follows that, by means of the described structure, it is alsopossible to reduce the wear of the tire at the lateral parts of tread 3.

Although the invention has been described in detail for the purpose ofillustration, it is to be understood that such detail is solely for thatpurpose and that variations can be made by those skilled in the artwithout departing from the spirit and scope of the invention except asit maybe limited by the claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A radial tire for vehicles comprising:

a carcass with sidewalls which have a curved external profile incross-section;

a tread between the sidewalls and having an external profile which iscurved in cross-section;

a breaker between the tread and the underlying carcass;

at the point of intersection between each sidewall and the tread, aright circular conical surface of rov tation having its axis coincidentwith the axis of the tire, said conical surface comprising a continuousannular band integral with the tread and having a surface which lies ina plane at an angle of from 15 to 50 with the tangent of the treadsprofile;

a plurality of circumferentially equally spaced radial grooves in saidconical surface; and

an annular groove coaxial with the axis of the tire in said conicalsurface;

said breaker extending beyond the point of intersection of the conicalsurface with the tread but not beyond the point of intersection of saidconical surface with said annular groove on that side of the groovewhich is axially nearer to the equatorial plane of the tire.

2. The tire of claim 1 wherein the width of the breaker is such thateach of its ends extend as far as the point of intersection of saidconical surfaces with said annular groove which is axially nearer to theequatorial plane of the tire.

3. The tire of claim 1 wherein the ratio of the width of the open end ofthe annular groove to the width of the conical surface is between 0.3and 0.6.

4. The tire of claim 1 wherein the depth of the annular groove is 0.2 to0.5 of the width of the open end of the groove.

5. The tire of claim 2 wherein each of said radial grooves terminatesatone end at the said point of intersection and terminates at theopposite end of the said sidewall.

6. The tire of claim 1 wherein the tread has cavities therein and thedepth of the cavities is such that a line concentric with the profile ofthe tread in cross-section passes through the point of intersection ofthe conical surface with the sidewalls.

1. A radial tire for vehicles comprising: a carcass with sidewalls whichhave a curved external profile in cross-section; a tread between thesidewalls and having an external profile which is curved incross-section; a breaker between the tread and the underlying carcass;at the point of intersection between each sidewall and the tread, aright circular conical surface of rotation having its axis coincidentwith the axis of the tire, said conical surface comprising a continuousannular band integral with the tread and having a surface which lies ina plane at an angle of from 15* to 50* with the tangent of the tread''sprofile; a plurality of circumferentially equally spaced radial groovesin said conical surface; and an annular groove coaxial with the axis ofthe tire in said conical surface; said breaker extending beyond thepoint of intersection of the conical surface with the tread but notbeyond the point of intersection of said conical surface with saidannular groove on that side of the groove which is axially nearer to theequatorial plane of the tire.
 2. The tire of claim 1 wherein the widthof the breaker is such that each of its ends extend as far as the pointof intersection of said conical surfaces with said annular groove whichis axially nearer to the equatorial plane of the tire.
 3. The tire ofclaim 1 wherein the ratio of the width of the open end of the annulargroove to the width of the conical surface is between 0.3 and 0.6. 4.The tire of claim 1 wherein the depth of the annular groove is 0.2 to0.5 of the width of the open end of the groove.
 5. The tire of claim 2wherein each of said radial grooves terminates at one end at the saidpoint of intersection and terminates at the opposite end of the saidsidewall.
 6. The tire of claim 1 wherein the tread has cavities thereinand the depth of the cavities is such that a line concentric with theprofile of the tread in cross-section passes through the point ofintersection of the conical surface with the sidewalls.